Physical Activity Minimum Threshold Predicting Improved Function in Adults With Lower-Extremity Symptoms

Objective: To identify an evidence-based minimum physical activity threshold to predict improved or sustained high function for adults with lower-extremity joint symptoms. Methods: Prospective multisite data from 1,629 adults, age ≥49 years with symptomatic lower-extremity joint pain/aching/stiffness, participating in the Osteoarthritis Initiative accelerometer monitoring substudy were clinically assessed 2 years apart. Improved/high function in 2-year gait speed and patient-reported outcomes (PROs) were based on improving or remaining in the best (i.e., maintaining high) function quintile compared to baseline status. Optimal thresholds predicting improved/high function were investigated using classification trees for the legacy federal guideline metric requiring 150 minutes/week of moderate-vigorous (MV) activity in bouts lasting 10 minutes or more (MV-bout) and other metrics (total MV, sedentary, light intensity activity, nonsedentary minutes/week). Results: Optimal thresholds based on total MV minutes/week predicted improved/high function outcomes more strongly than the legacy or other investigated metrics. Meeting the 45 total MV minutes/week threshold had increased relative risk (RR) for improved/high function (gait speed RR 1.8, 95% confidence interval [95% CI] 1.6, 2.1 and PRO physical function RR 1.4, 95% CI 1.3, 1.6) compared to less active adults. Thresholds were consistent across sex, body mass index, knee osteoarthritis status, and age. Conclusion: These results supported a physical activity minimum threshold of 45 total MV minutes/week to promote improved or sustained high function for adults with lower-extremity joint symptoms. This evidence-based threshold is less rigorous than federal guidelines (≥150 MV-bout minutes/week) and provides an intermediate goal towards the federal guideline for adults with lower-extremity symptoms.